An access orifice such as an eyehole, an armhole, or a manhole (where these terms distinguish orifices of different sizes) has a gasket face, i.e. a face which negages a gasket when the orifice is closed by means of a cover or door. In use, this face needs to be cleaned so as to obtain a gasket face whose surface state is as close as possible to the mating face of the cover so as to avoid the gasket creeping on being compressed as the cover is clamped into position. The surface state naturally varies as a function of the type of gasket used, but a good match between the gasket face and the cover is essential for good performance of the gasket, in particular in applications presenting severe or aggressive conditions.
Several brushing devices have already been proposed, suitable for brushing gasket faces of various sizes.
A distinction needs to be made between end brushing techniques and tangential brushing techniques. In an end brushing device, the axis of the brush is perpendicular to the gasket face and the bristles of the brush are disposed end-on, i.e. they run parallel to the axis of the brush. In contrast, in a tangential brushing device, the axis of the brush runs parallel to the gasket face and the bristles of the brush radiate, i.e. they are disposed radially relative to the brush axis. In any event, it is necessary in both cases to set up relative displacement between the brush axis and the gasket face to be brushed and this displacement must be as uniform as possible in order to obtain high quality brushing.
Brushing machines providing end-on brushing have existed for a long time, in particular sanding machines and polishing machines. Reference can made, for example, to French patent number 631 992 which describes a machine for polishing, waxing, and brushing floors, or to U.S. Pat. No. 2 668 968 which describes a sanding machine having a plurality of rotary brushes which are driven simultaneously by means of an associated gear train.
However, these are hand-held machines which are not suitable for brushing a manhole for gaining access to the inside of a vessel, particularly in a nuclear power station. The gasket face must be brushed extremely carefully, and facing sealing surfaces must be cleaned in such a manner as to ensure that any possible deposit or encrustation is removed before the cover or door is put back into place to close the manhole. In addition, in such cases radioactive contamination limits the time a team can remain on site while brushing the gasket face. It is well known that people wearing protective clothing seek to stay for as short a time as possible in a zone which is radioactivity contaminated and this naturally does not encourage careful manual cleaning.
Brushing machines have therefore been proposed suitable for working automatically under highly satisfactory conditions with respect to the accuracy obtained. A typical example of such a machine is illustrated by French patent number 2 512 358 which describes a motor-driven apparatus mounted to slide in an axial direction (parallel to the axis of the manhole) and optionally in a radial direction prior to being locked in a cleaning position. The brush support then rotates over the gasket face and brush rotates simultaneously about is own axis.
Nevertheless, this apparatus suffers from numerous drawbacks.
The first drawback is inherent to the principle of end-on brushing, since this inevitably gives rise to cycloidal brushing lines which do not coincide with the traces of machining on the gasket face. This means that radial paths are marked which may generate cracking. Thus apparatuses of this type are not satisfactory for use with steam generators or pressurizers in nuclear power stations.
Another drawback lies in the fact that the equipment supporting the brush is not axially movable for displacing the brush parallel to the axis of the manhole. This means that brushing is initiated after the brush has previously been pressed against the gasket face to be brushed, thereby giving rise to a greater pressure force in the initial zone and as a result leaving traces of non-uniform brushing.
Another drawback lies in the drive method used. A belt drive is used for rotating the brush support. However, when working in a plane which is not horiziontal, and in particular when working in planes having a negative angle of inclination (working on a sloping undersurface of a vessel), this structure gives rise to an out-of-balance effect which makes it difficult to maintain uniform rotation of the brush support which means that brushing is not uniform, particularly since the out-of-balance effect is always the same at any one position on the gasket face.
Finally, machines of this type are difficult to put into place unless associated with a special positioning machine (as in FIG. 1 of French patent number 2 512 358) which is bulky and inconvenient. Self-contained positioning of the apparatus is done blind without axial or radial pre-centering taking place automatically. It is therefore necessary to perform a difficult initial centering operation so as to position the apparatus correctly before locking into place.
Machines for performing tangential brushing have also been proposed.
This principle is well known and has been used for a long time in lightweight apparatuses, e.g. for brushing the rims of car wheels (one such application is illustrated in U.S. Pat. No. 2 915 766).
Several attempts have been made to use this principle for brushing a gasket face, particularly on nuclear reactor vessels. Tangential brushing is the only way of obtaining circular brushing lines capable of coinciding with the machining marks, unlike end-on brushing, and this is immediately more satisfactory for this type of application.
Machines differ considerably depending on the size of the gasket face to be brushed.
A first type of tangential brushing machine has been proposed for very large diameters (e.g. 5 meters). A good illustration is to be found in U.S. Pat. No. 3 922 748. The machine described in this patent comprises a funnel-shaped support carrying a peripheral rack for driving the arm which carries the brush by means of an associated motor whose outlet shaft carries a gear wheel which meshes with said rack, the brush-carrying arm supporting the drive motor for the brush which is intended for cleaning two coaxial grooves, and which is pivotally mounted on the funnel-shaped support. Such a machine stays in place by gravity, given its great weight.
It will easily be understood that a machine of this type would be difficult to adapt to a manhole, a fortiori if the manhole lies in a plane which is not horizontal. In particular, cleaning a sloping underside of a vessel would require major clamping means for fixing the machine in place and would require the entire structure to be adapted so as to ensure that its rack drive would continue to work properly. Further, the brush-carrying arm is pressed against the surface to be brushed solely by its own weight, and no means are provided for adjusting the force with which it is pressed against the surface.
The above-mentioned machine can therefore be considered only for special types of application, of large dimensions and having surfaces to be brushed which are essentially horizontal, and in addition not requiring very accurate brushing.
Another type of tangential brushing machine has been proposed for small diameters, and this considerably improves the performance of the preceding machine, while having a structure which is much more compact and convenient for handling. A typical example of such a machine is described in French patent number 2 598 944.
This machine includes a hollow shaft mounted coaxially with the access orifice and housing a central shaft having two coaxial elements which are coupled by a flexible link. The central shaft drives the brush about its axis via an angle take-off by virtue of a single pneumatic motor which also drives the hollow shaft via an epicyclic gear train. The housing of the machine is assembled on a plate which is bolted to the vessel via a bayonet type mounting suitable for rapid fixing. The brush is traditionally capable of being raised or lowered against the gasket face to be brushed by means of a telescopic system constituting an actuator, and operating in on/off mode. In addition, when in the working position, a spring interposed between two telescopic elements serves to urge the brush against the gasket face.
Such a machine gives excellent results for orifices of small diameter, e.g. eyeholes (about 50 mm in diameter) or armholes (190 mm or 220 mm). However it is not well suited to larger diameters, in particular to manholes where the diameter is about 406 mm.
The telescopic structure including the angle take-off requires the brush to be highly excentric in position and this gives rise to large bending forces on the bearings. These forces necessarily give rise to unwanted play when the diameter of the orifice is large.
This machine also suffers from other drawbacks if the intended use is to brush the gasket face of a manhole.
Firstly, since all of the moving parts are driven by a single motor, the motor becomes heavy and bulky when high power is required, as turns out to be the case with such a structure for orifices having a diameter of more than 300 mm. In addition, the speed of rotation of the brush and of the support are necessarily at a set ratio to each other such that adjusting the ratio of these speeds necessarily requires gears to be changed and this constitutes a considerable drawback.
Further, sucking up (or blowing away) the debris is not made easy. A lateral opening is provided in the leading skirt in order to connect the chamber inside the skirt to a suction device. For large diameter orifices, the skirt delimits an enormous internal volume (for an orifice having a diameter of 406 mm, it is necessary to have a skirt with a diameter of about 600 mm) and this implies that the suction means must be very powerful in order to achieve a satisfactory result.
Further, the method of fixing on the bolted sole plate remains awkward in practice and is ill-adapted to the weight of a large machine. The process of installing the sole plate lengthens the time required for operations, and with vessels in nuclear power stations, this becomes incompatible with the dose rate around the gasket face.
Finally, the spring associated with the brush is not adjustable (and is difficult to make adjustable within the context of such a structure), yet it is also required to accommodate the play inherent to an out-of-balance system.
An object of the invention is to provide a brushing device enabling the gasket face of a manhole to be brushed uniformly and effectively by tangential type brushing, which device does not suffer from the drawbacks and limitations mentioned above for tangential brushing apparatuses.
Another object of the invention is to provide a brushing device which is simple in structure, fairly light, and suitable for being installed very quickly, even in a contaminated environment.
Another object of the invention is to provide a brushing device including various possible adjustments enabling the brushing process to be adapted as well as possible to operating conditions.
Another object of the invention is to provide a brushing device which is genuinely effective at sucking up (or blowing away) the debris due to cleaning, in particular when sucking up radioactive debris in a contaminated environment.